Process for preparing dyes and/or brightener formulations

ABSTRACT

The invention relates to optical brighteners that possess at least one free SO 3 H group and their use for whitening materials containing cellulose.

This application is a divisional of U.S. Ser. No. 09/399,248, filed Sep.20, 1999 now U.S. Pat. No. 6,241,786.

The invention relates to processes for preparing dyes and/or brightenerformulations.

EP-A-835 906 describes dispersions of optical brighteners having SO₃Hgroups for whitening paper. Since the synthesis salts obtained when thebrightener is prepared are very detrimental to the subsequentdissolution with sodium hydroxide, in terms of the maximum brightenerconcentration possible, the salt content must be kept as low as possibleeven in aqueous dispersions of optical brighteners having SO₃H groups.

In EP-A-835 906 desalination takes place, for example, by washing thebrightener presscake with demineralized water. Disadvantages of thisprocedure are on the one hand that a high product loss is suffered whenthe presscake is handled and on the other hand that only moderate andnon-reproducible desalination conditions are present owing to theformation of channels in the presscake, as a result of which effectivedesalination is locally restricted.

A process has now been found by means of which it is possible toovercome the above-described disadvantages of the prior art.

The invention therefore provides a process for preparing formulationscomprising dyes and/or brighteners which possess at least one free SO₃Hand/or COOH group, characterized in that an aqueous suspensioncomprising

a) dyes and/or brighteners which possess at least one free SO₃H and/orCOOH group and

b) inorganic synthesis salts

is desalinated using a microfiltration membrane having pore diameters offrom 0.05 to 40 μm.

The dyes and/or brighteners having at least one free SO₃H and/or COOHgroup can of course also be present together with their salt forms (forexample alkali metal, alkaline earth metal or ammonium salts). It ispreferred, however, if at least one dye and/or brightener is present inthe form of its free acid to the extent of at least 90 mol-%.

The microfiltration membrane employed can be operated, for example, inthe cross-flow mode.

For cross-flow membrane filtration it is preferred to employ microporousmembranes as capillaries, tubes and in spiral-wound modular form. Themembranes are produced, for example, from inorganic (e.g. TiO₂, ZrO₂,Al₂O₃) or organic materials (e.g. propylene or partly fluorinated orperfluorinated polymers, polysulphone, polyether sulphone), the porediameters preferably being from 0.05 to 3.0 μm. A feature of thecross-flow mode is that the membranes are traversed tangentially by theproduct solution/suspension. In this context it is preferred to applytransmembrane pressures of from 1 to 10 bar. It is likewise preferred toconduct a periodic backwash from the permeate side in order to maintainhigh permeate performances.

The process of the invention operates with particular advantage if thepH of the suspension to be desalinated is from 1 to 6, in particularfrom 2 to 5.

It is likewise advantageous if the acid form (SO₃H and/or COOH) of thedye or brightener has a water solubility of less than 5 g/l, preferablyless than 1 g/l under the respective process conditions.

The process of the invention is preferably used to desalinateSO₃H-containing dyes and/or brighteners, especially brighteners.

The preferred amount of dye and/or brightener in the aqueous suspensionto be desalinated is from 100 to 500 g/l, in particular from 150 to 400g/l of aqueous suspension to be desalinated. At the same time theinorganic salt content in the suspension prior to desalination isgenerally from 1 to 25, preferably from 2 to 8% by weight, based on thesuspension. The inorganic salt content to be established preferably, bymeans of the process of the invention, is <1% by weight, in particularless than 0.5% by weight. The inorganic synthesis salt preferablycomprises alkali metal halides, sulphates or hydrogen sulphates.

The desalination of the invention takes place preferably at atemperature from 25 to 70° C., in particular at from 30 to 50° C.

The desalination can be operated with concentration or as diafiltration.In the case of diafiltration, the permeate formed is replacedcontinuously by demineralized water.

Optical brighteners employed in connection with the process of theinvention are with particular preference those of the formulae (I), (II)and/or (III):

in which

M represents H,

R₁ and R₂ independently of one another denote —NH₂, —NHCH₃, —NHC₂H₅,—N(CH₃)₂, —N(C₂H₅)₂, —NHCH₂CH₂OH, —NHCH₂CH₂CH₂OH, —N(CH₂CH₂OH)₂,—N(CH₂CH₂CH₂OH)₂, —N(CH ₃)(CH₂CH₂OH), —NHCH₂CH₂OCH₂CH₂OH,—NHCH₂CH₂CH₂SO₃M, —OH, —OCH₃, —OCH(CH₃)₂, —OCH₂CH₂OCH₃,

in which

M is as defined;

or of the formula

in which

R₃ is hydrogen, alkyl of 1 to 4 carbon atoms, alkoxy of 1 to 4 carbonatoms, halogen or SO₃M, and

R₄ is hydrogen or alkyl having 1 to 4 carbon atoms and

M is as defined;

and also the formula

in which

M is as defined and

R₅ and R₆ independently of one another denote hydrogen, CH₃,

or

R₅ and R₆ together complete a benzene ring.

Very particular preference is given to such brighteners of the formula(I), especially those of the formula (Ia)

It is likewise advantageous to append to the process of the invention aconcentration by means, for example, of membrane dewatering.

Prior to, during or after the process of the invention it is possible ifdesired to adjust the particle size of the dye dispersion or brightenerdispersion by means of a wet comminution technique, such as, forexample, Cavitron milling, jet disperser technology, beadmilling, etc.

The dye dispersions and/or brightener dispersions obtained in accordancewith the process of the invention can be mixed and/or homogenized, forexample following the addition of further additives such aspolyvinylpyrrolidone, commercially customary anionic dispersants, forexample formaldehyde-naphthalenesulphonic acid condensates or othercondensation products of aromatic sulphonic acids and formaldehydes, orstarch degradation products, such as anionic polyhydroxy compounds, forexample, preferably xanthan, and can then be used for dyeing orwhitening paper pulps in papermaking and for whitening or dyeing thecoating slips which are commonly used in the paper industry, the latterbeing unpigmented or, preferably, pigmented pulps and slips.

Reducing agents and preservatives may also be mentioned as furtheradditives, however.

Brighteners are preferably applied by three methods in papermaking:

Pulp: This is the cellulose suspension before the paper is made. Here itis preferred to employ the brighteners having 2 sulpho groups.

Coating slip, coating: Here, a coating is applied to the finished paperafter the drying section. In addition to optical brighteners, preferablythose having 6 sulpho groups, the coating slip comprises, inter alia,pigments (chalk, clay), latex binders, cobinders and dispersants.

Size press: After the drying section, paper which is almost finishedruns through the size press, which may consist, for example, ofcounterrotating rolls, which in turn run through a sump containingstarch and optical brightener. Alternatively, the application can bemade via a padder or by spraying, preferably followed by a dryingsection.

For the application of the dye dispersions and/or brightener dispersionsprepared in accordance with the process of the invention, an alkaline pHis advantageous for unhindered dissolution. In the case of coatingslips, this pH should in particular lie within the range from 8 to 11,and in the pulp should in particular be from 7.5 to 9. The desired pHcan be established, for example, by adding NaOH, in which case this pHis preferably established in the fiber dispersion or in the coating slipprior to the addition of the brightener dispersion. When using alkalinefillers, such as precipitated or natural calcium carbonate, it ispossible to dispense with the addition of alkali.

It is possible to improve not only the preparation of SO₃H— and/orCOOH-containing dyes and brightener formulations but also thepreparation of their salts, especially their aqueous solutions.

At the end of the synthesis, water-soluble organic dyes and brightenersare generally obtained in the form of dilute aqueous solutions which arecontaminated with by-products and which also still contain, depending onthe synthesis, inorganic salts, examples being alkali metal chloridesand sulphates. In order to produce ready-to-sell preparations from suchcrude solutions, they must be concentrated and freed as far as possiblefrom salts and by-products. A high salt content has an adverse effectabove all on the durability of liquid formulations, while by-products,which often also possess an intrinsic colour, may lead to a shift inshade. Membrane techniques for purifying such dye salts and brightenersalts have already been disclosed. It is common to operate withsolutions, i.e. in comparatively low concentrations, using preferablymembranes having a sufficient retention for the dissolved species (UF,NF). Ultrafiltration (UF) and nanofiltration (NF) membranes requireoperating pressures of more than 10 bar and so entail high operatingcosts. EP-A 197 006 has already described processes for purifying suchdye suspensions and brightener suspensions. The disadvantage: atwo-stage membrane technique is operated, with different MWCOs. The highresidual solubilities of the alkali metal salts employed (anionicdyes/brighteners) make it indispensable to use UF+NF membranes, with thedisadvantages described above.

The object of the present invention is to improve the existingseparation techniques. The aim is above all to achieve a highthrough-flow rate at low operating pressures, improved desalinationperformance, and, in general terms, high operational reliability.

The invention therefore additionally provides a process for preparingformulations of anionic dyes and/or brighteners which possess at leastone group SO₃M and/or COOM in which M denotes alkali metal or ammonium,characterized in that

i) an aqueous suspension comprising

a) dyes and/or brighteners which possess at least one free SO₃H and/orCOOH group and

b) inorganic synthesis salts is desalinated using a microfiltrationmembrane having pore diameters of from 0.05 to 40 μm and

ii) following the desalination, the suspended dye and/or brightener isdissolved by adding alkali metal or ammonium hydroxide, carbonate and/orhydrogen carbonate, and/or amines, and

iii) the dye solution and/or brightener solution obtained in accordancewith ii), directly or following the addition of further additives,especially solvents, is freed from colloidal and/or insolubleconstituents using a microfiltration membrane having pore diameters offrom 0.05 to 40 μm.

For substep i) of this process the ranges of preference are the same asfor the process of the invention for preparing SO₃H— and/orCOOH-containing dyes and/or brighteners.

For substep ii) of the process of the invention it is preferred to useNaOH, LiOH, KOH, K₂CO₃, Na₂CO₃, NR₁R₂R₃R₄OH, NR₁R₂R₃, where R₁, R₂, R₃and R₄ independently of one another denote H, alkyl, aryl (optionallysubstituted) in order to dissolve the dispersed dye and/or brightener.Preference is given to KOH, LiOH, N(CH₃)₄OH, H₂NCH₂CH₂OH, HN(CH₂CH₂OH)₂and H₂NCH₂CH₂NHCH₂CH₂OH.

In substep ii) it is possible if desired to add one or more solubilizerssuch as, for example, ε-caprolactam, urea, triethylene glycol,polyethylene glycol, propanediol, 1-ethoxy-2-propanol and/or diethyleneglycol. For the choice of the base(s) employed it is possible todetermine the counterion for the anionic dye and/or brightener.

For substep iii) of the process of the invention the microfiltrationmembranes employed are preferably those as have already been describedabove. The membranes used in substeps i) and iii) are independent of oneanother. They can be identical but need not be so. It is thereforeentirely possible to employ a different membrane material and/or adifferent modular form than for substep i). Preferably, however, themembranes employed for substep iii) possess pore sizes which are greaterthan the size of the anionic optical brightener and/or dyes, or thesolution aggregates thereof. Substep iii) is preferably operated as adead-end filtration.

“Dead-end” mode means that the membrane or membrane filter is nottraversed tangentially during most of the permeation period. Forexample, cross-flow apparatuses can be utilized in the manner indicatedif the retentate side is completely closed and is opened only for briefperiods in order to discharge retained particles.

Colloid and/or insoluble constituents are preferably separated off at atemperature of from 40 to 100° C., preferably at from 50 to 80° C.

By an appropriate choice of membrane for substep iii), preferably withpore diameters <0.2 μm, this filtration can also be carried out as asterile filtration.

The dye solution or brightener solution obtained after substep iii) ofthe process of the invention can be dried to a solid (powder orgranular) dye or brightener preparation by removal of water, optionallyfollowing the addition of formulation auxiliaries, or can be usedfurther as a stable liquid formulation, optionally following theaddition of formulation auxiliaries such as solubilizers (urea, ureaderivatives, glycols, polyglycols, alkanolamines, lactams such asε-caprolactam, etc.).

The invention further relates to the brightener of the formula Ia as thebis-^(⊕)N(CH₃)₄ salt (Ib) and as the bis-^(⊕)H₂N(CH₂CH₂OH)₂ salt (Ic).

The invention additionally relates to the use of the brightener offormula Ia as the bis-^(⊕)H₃NCH₂CH₂OH salt (Id) and as the bis-H₃^(⊕)NCH₂CH₂NHCH₂CH₂OH salt (Ie) for whitening materials containingcellulose, especially paper.

The brightener salts Ib and Ic of the invention, and also the brightenersalts Id and Ie used in accordance with the invention, are suitable forwhitening paper pulps in papermaking, examples being cellulose, woodpulp (chemical and mechanical pulp) and for whitening the coating slipscommonly used in the paper industry, specifically for whiteningunpigmented or, in particular, pigmented pulps and slips.

The known coating slips comprise as binders, inter alia, polymerdispersions based on copolymers of butadiene-styrene,acrylonitrile-butadiene-styrene, acrylates, ethylene-vinyl chloride orethylene vinyl acetate, or based on homopolymners, such as polyvinylchloride, polyvinylidene chloride, polyethylene, polyvinyl acetate orpolyurethanes. A preferred binder consists of styrene-butyl acrylate orstyrene-butadiene-acrylic acid copolymers. Further polymer latices aredescribed, for example, in U.S. Pat. No. 3,265,654.

The coating slips are commonly pigmented using aluminium silicates, suchas china clay and kaolin, and also barium sulphate, satin white,titanium dioxide or calcium carbonate (chalk).

The coating slips of the invention contain preferably from 5 to 70% byweight of a white pigment. The binder is preferably used in an amountwhich is sufficient for the dry content of polymeric compound to be from1 to 30% by weight, preferably from 5 to 25% by weight of the whitepigment. The amount of the brightener dispersion of the invention iscalculated such that the brightener is present in amounts of from 0.005to 1% by weight, in particular from 0.01 to 0.55% by weight, based onwhite pigment.

The coating slip of the invention can be prepared by mixing thecomponents in whatever order at temperatures from 10 to 100° C.,preferably from 20 to 80° C. The components here also include thecustomary auxiliaries which can be used to regulate the rheologicalproperties, such as viscosity or water retention capacity, of thecoating slips. Examples of such auxiliaries are natural binders, such asstarch, casein, protein or gelatine, cellulose ethers, such ascarboxyalkylcellulose or hydroxyalkylcellulose, algic acid, alginates,polyethylene oxide or polyethylene oxide alkyl ethers, copolymers ofethylene oxide and propylene oxide, polyvinyl alcohol,polyvinylpyrrolidone, water-soluble condensation products offormaldehyde with urea or melamine, polyphosphates or polyacrykic salts.

The brighteners of the formula Ib, Ic, Id and Ie to be used inaccordance with the invention are incorporated either into the finishedcoating slip or into one of the components of the coating slip.

The coating slip of the invention can be used for coating paper, wood,films, such as cellulose, cellulose triacetate, textile materials, etc.Particular preference is given to its application to paper and cardboardand also photographic papers.

The coating slip can be applied to the substrate by any conventionaltechnique: for example, using an air knife, a spreading knife, a brush,a roller, a doctor blade or a rod, after which the coating is dried,using for example an infrared dryer and/or hot-air dryer, attemperatures of the substrate surface in the range from 70 to 200° C.,preferably from 90 to 130° C., down to a residual moisture content offrom 3 to 6% by weight.

For the use of the coating slips of the invention, the coatings obtainedfeature optimum distribution of the optical brighteners over the entiresurface and, consequently, an increase in whiteness and also high lightfastness.

EXAMPLES Example 1

In each case 30 kg of a synthesis suspension of a disulpho opticalbrightener of the formula (Ia) having a dry matter content of 13% and asodium chloride content of 5.5% are concentrated and desalinated on amicrofiltration unit at a pH of from 3 to 4.5. Polymer membranes madefrom polyvinylidene fluoride (PVDF) are used, as tubular modules havinga diameter of ½″. The membrane has a pore width of 0.1 μm, the module anarea of 0.3 m².

Desalination/Concentration

Beginning at 20° C. and a module entry pressure of 5 bar, 15 kg ofpermeate are taken off first of all before diafiltration is conducted bytaking off 60 kg of permeate and continuously adding 60 kg ofdemineralized water. In the course of this diafiltration, the operatingtemperature is raised to 40° C.

Final concentration is carried out by removing 8 kg of permeate. Theretentate has a dry matter content of 33%. The residual NaCl content isabout 0.1%.

Clarifying Filtration

Following the end of desalination and concentration, the pressure isreduced to 0 bar. Subsequently, 10% by weight of diethylene glycol and3% of diethanolamine are added. The suspension is heated to 55° C. anddissolved by adding

a) Potassium hydroxide solution at a pH of 9.5. The transmembranepressure is then raised to 10 bar and the permeate obtained is the clearbrightener solution. Following standardization (addition ofdemineralized water until a 1% solution in water has an extinction of135; path length 1 cm, wavelength 340 nm) the result is a highlyconcentrated liquid formulation which shows no instances ofprecipitation, etc., even after storage for 5 months at RT and 0° C.

b) Sodium hydroxide solution at a pH of 9.5. The transmembrane pressureis then raised to 10 bar and the permeate obtained is the clearbrightener solution. Following standardization the result is a liquidformulation from which first crystals of product deposit after storagefor 3 months at 0°C.

c) Lithium hydroxide at a pH of 9.5. The transmembrane pressure is thenraised to 10 bar and the permeate obtained is the clear brightenersolution. Following standardization the result is a liquid formulationfrom which first crystals of product deposit after only a week at roomtemperature.

Example 2

30 kg of a synthesis suspension of the disulpho optical brightener ofthe formula Ia having a dry matter content of 14% and a sodium chloridecontent of 4.5% are concentrated and desalinated on a microfiltrationunit at a pH of from 3 to 4.5. A ceramic capillary module is used,having a channel height of 4 mm, a membrane surface area of 0.059 m² anda pore width of 0.5 μm.

Desalination/Concentration

At 25-30° C. and a module entry pressure of 2.0 bar, 18 kg of permeateare taken off first of all before diafiltration is conducted by takingoff 30 kg of permeate and continuously adding 30 kg of demineralizedwater. Final concentration is carried out by removing 3 kg of permeate.The retentate has a dry matter content of 29%. The residual NaCl contentis about 0.2%.

Clarifying Filtration

Following the end of desalination and concentration, the pressure isreduced to 0 bar. Subsequently, 10% by weight of triethylene glycol and3% of triethanolamine are added. The suspension is heated to 60° C. anddissolved by adding potassium hydroxide solution at a pH of 9. Thetransmembrane pressure is then raised to 3 bar and the permeate obtainedis the clear brightener solution. Following standardization, the resultis a storage-stable highly concentrated liquid formulation.

Example 3

12 kg of the same brightener suspension as in Example 2 are treatedusing a tubular module of polypropylene having a membrane surface areaof 0.036 m² and a pore width of 0.2 μm. In contradistinction to Example2, the module is periodically backwashed with permeate.

Desalination/Concentration

30° C. and a module entry pressure of 2.0 bar, 5 kg of permeate aretaken off first of all before diafiltration is conducted by taking off21 kg of permeate and continuously adding 21 kg of demineralized water.Final concentration is carried out by removing 2 kg of permeate. Theretentate has a dry matter content of 27%. The residual NaCl content isabout 0.1%. The specific permeate flow here, at about 400 kg(m²h), isabout twice as high as in the first example.

Clarifying Filtration

Following the end of desalination and concentration, the transmembranepressure is reduced to 0 bar. Subsequently, 10% by weight of triethyleneglycol are added. The suspension is heated to 50° C. and largelydissolved by adding potassium hydroxide solution at a pH of 9. Thetransmembrane pressure is then raised to 3 bar and the permeate obtainedis the clear brightener solution. Following standardization, the resultis a storage-stable highly concentrated liquid formulation.

Example 4

The retentate from Example 3 is heated to 55° C. after the end ofdesalination and concentration, and is substantially dissolved by addingtetranethylammonium hydroxide at a pH of 9.4. Clarifying filtrationthrough a 1.2 μm membrane filter in dead-end operation gives a clearsolution which has an extraordinarily good storage stability incomparison to the corresponding alkali metal salt formulations(comparable foreign electrolyte content).

Example 5

The retentate from Example 3 is heated to 55° C., after the end ofdesalination and concentration, and is substantially dissolved by addingethanolamine at a pH of 8.7. A clarifying filtration through a 1.2 μmmembrane filter in dead-end operation separates off a few insolubleconstituents. The clear solution has a good stability on storage whichis comparable with that of Example 4.

Example 6

The retentate from Example 3 is admixed with 20% of diethylene glycolfollowing the end of desalination and concentration and is substantiallydissolved at room temperature by adding 2-(2-aminoethylamino)ethanol ata pH of 9.5. A clarifying filtration through a 5 μm membrane filter indead-end operation separates off insoluble constituents. The clearsolution has excellent storage stability.

Example 7

A solution virtually free of foreign salt, comprising the lithium/sodiummixed salt (molar ratio about 1:1) of the phthalocyanine dye Direct Blue199, is admixed with sulphuric acid to a pH of 1.0. The suspension isthen desalinated twice by diafiltration using a tubular membrane havinga pore width of about 50 nm.

Direct Blue 199 has the formula

The corresponding ethanolammonium salts were obtained analogously byusing the following ethanolamines in place of LiOH:

6a: H₂N CH₂CH₂OH

6b: HN (CH₂CH₂OH)₂

6c: N (CH₂CH₂OH)₃

The dye salts of Example 6 are outstandingly suitable for dyeing andprinting paper, especially for printing by the ink-jet method.

What is claimed is:
 1. A compound of the formula

wherein M represents H₂ ^(⊕)N(CH₂CH₂OH)₂.
 2. A method for whiteningmaterials containing cellulose comprising applying to said materials acompound of the formula

wherein M represents H₂ ^(⊕)N(CH₂CH₂OH)₂, H₃ ^(⊕)NCH₂CH₂OH, and/or H₃^(⊕)NCH₂CH₂NHCH₂CH₂OH.